Captives at Guantánamo Bay were chained hand and foot in a fetal position to the floor for 18 hours or more, urinating and defecating on themselves, an FBI report has revealed.

The accounts of mistreatment were contained in FBI documents released yesterday (pdf) as part of a lawsuit involving the American Civil Liberties Union, a civil liberties group.

In the 2004 inquiry, the FBI asked nearly 500 employees who had served at Guantánamo Bay to report possible mistreatment by law enforcement or military personnel. Twenty-six incidents were reported, some of which had emerged in earlier document releases.

Besides being shackled to the floor, detainees were subjected to extremes of temperature. One witness said he saw a barefoot detainee shaking with cold because the air conditioning had bought the temperature close to freezing.

On another occasion, the air conditioning was off in an unventilated room, making the temperature over 38C (100F) and a detainee lay almost unconscious on the floor with a pile of hair next to him. He had apparently been pulling out his hair throughout the night.

In October 2002, one interrogator squatted over a copy of the Qur'an during intensive questioning of a Muslim prisoner, who was "incensed" by the tactic, according to an FBI agent.

On another occasion, an agent was asked by a "civilian contractor" to come and see something.

"There was an unknown bearded longhaired d (detainee) gagged w/duct tape that had covered much of his head," the FBI document said.

When the FBI officer asked if the detainee had spit at interrogators, the "contractor laughingly replied that d had been chanting the Qur'an non-stop. No answer how they planned to remove the duct tape," the report said.

After an erroneous report of Qur'an abuse prompted deadly protests overseas in 2005, the US military conducted an investigation that confirmed five incidents of intentional and unintentional mishandling of the book at the detention facility.

It acknowledged that soldiers and interrogators had kicked the Qur'an, had stood on it and, in one case, had inadvertently sprayed urine on a copy.

An FBI agent called W also heard that female interrogators would sometimes wet their hands and touch detainees' faces in order to disrupt their prayers. Such actions would make some Muslims consider themselves unclean so they would stop praying.

The detention of terrorist suspects at Guantánamo Bay has been strongly criticised by human rights groups. In a rebuff for the Bush administration, the US supreme court last year rejected its claims that detainees at the facility were not entitled to the protection under the Geneva convention.

The department of defence consequently issued a memo stating that prisoners would in the future be entitled to such protection. As of November 2006, out of 775 detainees who have been brought to Guantánamo, approximately 340 had been released, leaving 435 detainees.

Of those 435, 110 have been labelled as ready for release. Of the other 325, only about 70 will face trial by military commissions, criminal courts run by the US armed forces. That leaves about 250 who may be held indefinitely.